(1) Field of the Invention
The present invention relates to a turbine engine component having improved cooling and a refractory metal core for forming the cooling passages.
(2) Prior Art
Rotational speeds for certain types of engines are very high as compared to large commercial turbofan engines. As a result, the main flow through the cooling circuits of turbine engine components, such as turbine blades, will be affected by secondary Coriolis forces and rotational buoyancy. The velocity profile of the main cooling flow is towards the trailing edge of the cooling passage. For a radial outward flow cooling passage with an aspect ratio of 3:1, there is a strong potential for cooling flow reversal, which in turn leads to poor heat transfer performance. Therefore, it is extremely important for cooling passages to maintain aspect ratios as close as possible to unity. This is needed to avoid main flow reversal and poor heat transfer performance.
There are existing cooling schemes currently in operation for different small engine applications. Even though the cooling technology for these designs has been very successful in the past, it has reached a culminating point in terms of durability. That is, to achieve superior cooling effectiveness, these designs have included many enhancing cooling features such as turbulating trip strips, shaped film holes, pedestals, leading edge impingement before film, and double impingement trailing edges. For these designs, the overall cooling effectiveness can be plotted in durability maps as shown in FIG. 1, where the abscissa is the overall cooling effectiveness parameter and the ordinate is the film effectiveness parameter. The plotted lines correspond to the convective efficiency values from zero to unity. The overall cooling effectiveness is the key parameter for a blade durability design. The maximum value is unity, implying that the metal temperature is as low as the coolant temperature. This is impossible to achieve. The minimum value is zero where the metal temperature is as high as the gas relative temperature. In general, for conventional cooling designs, the overall cooling effectiveness is around 0.50. The film effectiveness parameter lies between full film coverage at unity and complete film decay without film traces at zero film.
The convective efficiency is a measure of heat pick-up or performance of the blade cooling circuit. In general, for advanced cooling designs, one targets high convective efficiency. However, trades are required as a balance between the ability of heat pick-up by the cooling circuit and the coolant temperature that characterizes the film cooling protection to the blade. This trade usually favors convective efficiency increases. For advanced designs, the target is to use design film parameters and convective efficiency to obtain an overall cooling effectiveness of 0.8 or higher, as illustrated in FIG. 1. From this figure, it is noted that the film parameter has increased from 0.3 to 0.5, and the convective efficiency has increased from 0.2 to 0.6. As the overall cooling effectiveness increases from 0.5 to 0.8, this allows the cooling flow to be decreased by about 40% for the same external thermal load. This is particularly important for increasing turbine efficiency and overall cycle performance.